Rotation devices are known in many embodiments.
A centrifugal pump is for instance known with an axial inlet and a rotor with blades for flinging a liquid for pumping radially outward under the influence of centrifugal forces, and one or more for instance tangential outlets.
Further known is an axial compressor having groups of rotor and stator blades ordered in cascade. The structure comprises many thousands of components of extremely complex form which must moreover comply with high standards of dimensional accuracy and mechanical strength. An example hereof is a gas turbine, wherein in this case gaseous medium under pressure is delivered by a source intended for this purpose and is directed onto the blades of a rotor such that this rotor is driven with force, for instance to rotatingly drive a machine such as an electric generator.
These known devices display flow instabilities, particularly at low flow rates. These usually cause an imbalance in the rotor load which gives rise to heavy vibrations, uncontrollable variations in rotation speed and very heavy mechanical loads on bearings, shafts and blades.
All known rotation devices also have further certain technical shortcomings.
The efficiency is for instance often relatively low and greatly dependent on the speed of rotation.
The known devices are moreover usually voluminous, heavy and expensive.
In the use of casting techniques to manufacture a rotor the blades must have a certain minimal wall thickness, which gives rise to undesirable reductions in the effective through-flow volume and losses due to release and wake-forming. The blade wall thickness and the required blade form moreover limit the number of blades which can be accommodated. In addition, the casting technique unavoidably results in undesired surface roughness and imbalance as a consequence of unintended and unmanageable differences in density, for instance as a result of inclusions.
The tensile strength of cast metals and alloys is also limited.
Known centrifugal pumps are further affected by so-called slippage, the phenomenon of the flow having little adhesion to the suction side of the flow channel bounded by adjoining blades. Owing to the expansion angle between the blades there is a slippage area or an area with xe2x80x9cstagnantxe2x80x9d water in which a large-scale stationary turbulence is located, whereby the through-flow in that area is zero. The outlet pressure of the centrifugal pump is strongly pulsating as a result.
In addition, known devices are constructed such that they produce a great deal of noise during operation.
All known devices operating for instance as water pumps have a limited pressure capacity. For applications as fire service pump for instance, pumps are therefore often placed in cascade with one another in order to realize the required pressure, also expressed as lift of the water for pumping.
In the known rotation devices it is sometimes also perceived as a drawback that medium inlet and medium outlet do not have the same direction but are directed for instance at right angles to each other. In determined conditions it may be desired to at least have the option of giving the inlet and the outlet the same direction.
Known devices are further unable to operate with media having greatly varying viscosities.
In known devices the flow speeds of the through-flowing media vary very considerably during through-flow of a device. Noise production and efficiency loss result as a consequence of the accelerations which occur. It would be desirable in this respect to keep the through-flow speed of media flowing through a rotation device constant under all conditions, for instance within a range of 0.2-5 times a target value.
It is an object of the invention to provide a rotation device which either does not possess the above stated problems and limitations of the prior art or at least does so to a lesser extent.
In respect of the above the invention generally provides a rotation device.
The device can for instance be employed as pump or compressor.
The device relates to a device operating as a motor.
The invention can relate to different media for pumping. The term xe2x80x9ctwo-phase mediumxe2x80x9d relates for instance to media which may be liquid and/or gaseous depending on operating temperature and operating pressure. Such media are much used in cooling systems. Examples are freons, ammonia, alkanes.
The present invention defines in general terms a possible form of the rotor channels and gives increasing preferences for the number of rotor channels.
The present invention relates to a structure of the rotation device which prevents strong periodic pressure pulsations during operation. Such a structure ensures a low-noise and uniform flow.
The invention further relates to the application of an infeed propellor in the medium inlet in the case of a rotation device serving as medium pump. The infeed propellor ensures that the medium enters the rotor channels without release at a certain pressure and speed.
A very practical embodiment relating to a light and easily manufactured rotor is described herein.
Since it is important that in the region of the third medium passage no discontinuity occurs which could cause large-scale swirling and turbulences, release and noise production, the structure according to the present invention can be advantageous.
The invention provides a structure of the rotation device wherein a relatively large number of baffles can be used without the thickness of the baffles at the position of the third medium passage substantially reducing the passage for medium at that position. As a result of the transverse dimension becoming wider in radial direction relative to the axial direction of the rotor channels, additional space is available for interwoven placing of a second group of second baffles at a distance from the third medium passage. As far as is necessary, a third group of baffles can also be placed between the interwoven first and second baffles. These baffles are in turn shorter than the second baffles and extend in the direction of the third to the fourth medium passages as far as the fourth medium passage at a distance from the end of the second baffles directed to the third medium passage. This structure enables a very good flow guiding without this essentially having an adverse effect on the effective passage of the medium.
The invention also relates to the form of the stator blades. Since all stator blades are placed in angularly equidistant manner, their mutual distance is always the same in any axial position. Rheologically however, it is essential that, as seen in the direction from the fifth medium passage to the sixth medium passage, an effective fanning out occurs in a direction as seen along a flow line in a stator channel. Perpendicularly of such a flow line an angle of progression can be defined at any position along this flow line between the blades. The structure has the advantage of a considerably improved efficiency.
The use of plate material for manufacture of the dishes and the blades according to the invention has the advantage that the rotor can be very light. Plate material can further be very light, smooth and dimensionally reliable. The choice of material will be further determined by considerations of wear-resistance (depending on the medium passing through), bending stiffness, mechanical strength and the like. For the rotor, the dishes of which have the described double-curved form, it is important that the principal form is retained, even when the material is subjected to centrifugal forces as a result of high rotation speeds. In this respect attention is drawn to the fact that the blades, which are arranged between the dishes and rigidly coupled thereto, contribute to a considerable degree towards stiffening of the rotor. For this reason also it is important to use a large number of blades. A rotor can also be manufactured with very high dimensional accuracy and negligible intrinsic imbalance.
The invention also provides options relating to choices of material under specific conditions.
Depending on the dimensions of the rotor and the rotation speed, the described plate material can have a desired value. An appropriate choice lies generally in the range stated herein. In respect of the possibility of a small imbalance, the mass moment of inertia of the rotor is preferably as small as possible, particularly in the case of media with low density such as gases. In this context it is recommended to choose the technically smallest possible thickness.
The invention provides several possible techniques with which the rotor baffles can be coupled to the dishes.
The invention provides possible choices of material for the stator blades. The technical considerations forming the basis of this choice are by and large the same as those for the rotor baffles.
The invention relates to the material choices of or at least the materials on the cylindrical inner surface of the housing and of the stator blades. By setting the thermal expansion coefficients of these materials, thermal stresses are avoided and it is ensured that the mutual connection and the correct shape of the stator channels also remain preserved in the case of extreme temperature variations.
The invention provides as a specific development of the described technical principle the possibility of the materials being the same. It will be apparent that in a further development not only the cylindrical inner surface of the housing must be of the relevant material but this can also be the case for the whole cylindrical jacket of the housing, or even the whole housing.
The invention relates to the form of the stator channels.
As already described above, the mass moment of inertia, and therewith the danger of a certain imbalance of the rotor, is preferably as small as possible.
The invention further relates to this same aspect and applies particularly to gas as medium, which after all makes no appreciable contribution to the mass moment of inertia. Although as a result of the small radial dimensions the shaft should have a considerable weight in order to have a mass moment of inertia in the same order of magnitude as that of the rotor, it should nevertheless be understood that the contribution in question can be substantial in respect of the length of the shaft which in some conditions is relatively great. In addition, the rotor will preferably take the lightest possible form so that for this reason its mass moment of inertia will also be relatively small.
The invention provides several possibilities for forming the rotor dishes.
The invention also provides a very specific method of forming a rotor.
Particularly in the case of a very hot or very cold medium, the structure according to an embodiment of the invention is significant.
The invention provides a very advantageous embodiment wherein an effective sealing is combined with a friction which practically amounts to zero.
The invention provides in increasing preference possible numbers of stator blades. In By the design of the rotation device according to the invention account must be taken of the fact that a local flow tube is then only controllable over a wide flow range if the flow tube is elongate.
The invention provides further characterizations of the rotation device in terms of the ratio of the total cross-sectional surface of all fourth medium passages and the third medium passage. The relevant choice is greatly dependent on design requirements.
The present invention further provides options relating to the ratio of the diameter of the ring of fourth medium passages and the diameter of the third medium passage. The relevant choice depends on the pressure ratio to be generated between the inlet and outlet in the case of a pump or the expansion ratio in the case of a turbine.
In the pump according to the inventio there is still strong rotation in the region of the fourth and fifth medium passages. This results locally in a relatively low static pressure, in contrast to the known centrifugal pump. As a resuly of the local relatively low pressure relatively small demands are made of the thicknesses of the relevant walls and the local seals, whereby use can for instance be made of simple seals such as labyrinth seals, which in particular conditions are considered low-grade. As is known, because of its nature a labyrinth seal is not completely closed. As a consequence of the relatively low local pressure the seal is nevertheless sufficient when labyrinth seals are used.
Said small wall thicknesses enable manufacture by deep-drawing.
The device according to the invention can be applied very widely. As pump it displays a very even pressure and efficiency characteristic and a more~or less monotonous power characteristic, whereby one pump is suitable for many very varied applications, while in usual pumps different dimensioning is required for different applications.
The said monotonous, substantially linear characteristic at any rotation speed provides the important option, by means of a very simple adjustment of the driving power, of achieving an output performance corresponding substantially unambiguously therewith. The prior art requires for this purpose a complicated and expensive adjustment based on the momentary values of a number of relevant parameters. This is the reason why such adjustments are not applied in practice.
For pumping of media with very varying viscosities only a limited number of differently dimensioned pumps is necessary as a consequence of the small dependence of the properties of the device on the viscosity of the medium.
In the use as pump, one device can realize a very large flow rate and/or a very high pressure comparable to the cascading of a plurality of pumps as according to the prior art.
In order to reverse the operation of a pump to that of a motor or vice versa, some modification of the dimensioning of stator channels and rotor channels will generally be desirable.